The simplest model of motion is for an object that moves in a straight line at constant speed. You can use this simple model to build your understanding about the basic ideas of motion, and the different ways in which you will represent that motion.

Displacement: A vector quantity that describes a change in position.

The displacement vector ($\Delta \vec{r}$) describes the change of an object's position in space. The displacement vector describes a change in location. So, you can think of it as displacement = change in position = final location - initial location. This is represented in the diagram to the right (Displacement figure). Mathematically, we represent the displacement like this:

$$\Delta \vec{r} = \vec{r}_f - \vec{r}_i$$